目录

__new__特殊方法实现

class Singleton:    def __new__(cls, *args, **kwargs):        if not hasattr(cls, '_instance'):            cls._instance = super(Singleton, cls).__new__(cls)        return cls._instance    def __init__(self, name):        self.name = names1 = Singleton('first')s2= Singleton('last')print(s1 == s2)>> Trueprint(s1.name)>> last

tips: __new__方法无法避免触发init()，初始的成员变量会进行覆盖

装饰器实现

def singleton(cls):    _instance = {}    def inner(*args, **kwargs):        if cls not in _instance:            _instance[cls] = cls(*args, **kwargs)        return _instance[cls]    return inner@singletonclass Test:    def __init__(self, name):        self.name = namet1 = Test('first')t2 = Test('last')print(t1==t2)>> Trueprint(t2.name)>> first

类装饰器实现

class Singleton:    def __init__(self, cls):        self._cls = cls        self._instance = {}    def __call__(self, *args):        if self._cls not in self._instance:            self._instance[self._cls] = self._cls(*args)        return self._instance[self._cls]@Singletonclass Cls2:    def __init__(self, name):        self.name = namecls1 = Cls2('first')cls2 = Cls2('last')print(id(cls1) == id(cls2))>> Trueprint(cls1.name)>> first

元类实现

class Singleton1(type):    def __init__(self, *args, **kwargs):        self.__instance = None        super(Singleton1, self).__init__(*args, **kwargs)    def __call__(self, *args, **kwargs):        if self.__instance is None:            self.__instance = super(Singleton1, self).__call__(*args, **kwargs)        return self.__instanceclass C(metaclass=Singleton1):    def __init__(self, name):        self.name = namec1 = C('first')c2 = C('last')print(c1 == c2)>> Trueprint(c2.name)>> first

模块实现

Python 的模块就是天然的单例模式，因为模块在第一次导入时，会生成 .pyc 文件，当第二次导入时，就会直接加载 .pyc 文件，而不会再次执行模块代码。

#foo1.pyclass Singleton(object):    def foo(self):        passsingleton = Singleton()#foo.pyfrom foo1 import singleton

部分内容参考自: